Biology of Hair and Nails Trichinosis Molecular and Cellular Pathology Dr Tim Scott-Taylor Health and Human Sciences.

Biology of Hair and Nails

Trichinosis Molecular and Cellular Pathology

Dr Tim Scott-Taylor Health and Human Sciences

Topics

Topics covered; the nature of hair follicles structure of keratin normal patterns of hair growth causes of hair lost

Tutorial; review of skin structure and function light microscopy

Learning Objectives

to know the nature of skin follicles and hair

growth

to know the function of hair in animals and

humans

to know the structure of hair fibres

to understand the causes and treatment of

hair loss

Hair

Longitudinal filamentous growth from the skin Composed of keratin Found mainly in mammals; definition of phylum Wool, fur, pelage

Function: insulation protection protective coloration ornamentation / communication sensory (vibrissae)

Skin and Keratin

Keratinized stratified squamous epithelium is found only in the skin

Keratin accumulation within maturing cells effectively waterproofs the cells, blocking diffusion of nutrients and wastes.  The cells subsequently die.

Hair is specialised adaptation of epithelial production of keratin

Keratocytes

• keratocytes are cells that make

keratins

• >40 highly insoluble proteins

forming a network in the cytoplasm

of keratocytes.

• transform from undifferentiated

basal cells to cornified skin cells.• four continuous layers basal

spinous granular cornified

recognizablehistologically

In the course of approximately 13 days columnar basal cells mature through a polygonal spinous cell, a diamond-shaped granular cell to a flat cornified cell that covers 25 basal cells.

Parts of Hair

Hair follicle; involution of epidermis

Root; implanted in skin

Shaft or scapus; projecting from

surface

hair Bulb; root enlargment, soft, white

Papilla; dermal, blood and nerves

Sebaceous glands; open into follicle

Arrector muscle; attached to

epidermis

Nails

Longitudinal section through nail and its nail

groove

Claws, Nails, Hooves and Spurs

Keratin structures found in all mammals except cetaceans (whales). Derived from reptile claws. Consist of dorsal unguis = nail plate

ventral subunguis = sole plate  a) claws - unguis is curved and encloses the subunguis

retractable in some carnivores.  b) hooves - Unguis completely surrounds subunguis.

cloven hooves in even-toed ungulates (Artiodactyls) c) spurs - in male monotremes a hollow keratin spur on hind legs

poison gland associated with it. d) nails - only in primates. Flat unguis + subunguis

greater precise manipulation of food or tools.  

Some Horns and antlers  rhino horn - mass of keratin threads produced by epidermis  bovid horn - bony core, horny sheath, no shedding pronghorn - bony core, horny sheath shed annually

Hair is a Defining Feature

Comparison Reptiles - Mammals 

Reptiles Mammals

scales

few epidermal glands

no mammary glands

3-chambered heart

ectothermy

little cerebral

development

indeterminate growth

egg laying

hair

many epidermal glands

mammary glands

4-chambered heart

endothermy

much cerebral

development

determinate growth

live birth

Hair is characteristic of the phylla

Temperature regulation was a fundamental development in mammalian evolution

Animal Hair

Fur, coat, pelage, wool: furry insulating covering Special adaptations; Spines; porcupine

Bristles; lion’s maneUV transporter; polar

bear dolphins, whales; aquatic adaptation

(otters and seals)

Size and hair; mass 1/ follicle per cm2

eg elephant, rhinoceros heat loss

Types of Animal Hair

Vibrissae; elongated + stiffenedassociaed with many nerve

fibers mainly tactile receptors

facial and carpalespecially in

carnivores

primatesrodentia

Underhair; main function is insulation.

a) wool long soft and curly angora

b) fur fine relatively short hairdefinitive growth

c) velli down or fuzz with velvety appearance  

Types of Animal Hair

Types of Animal Hair

Guard hair; long, straight and pointed overhairs present on most mammals

a) awns stiff intermediate sized hair, protects downb) spines enlarged, stiff guard hairs with finite growth

evolved parallel hedgehogs ~6 times in mammals spiny anteaters

tenrecs barbs porcupines

poisonous montremes

c) bristles long firm hair eg. horse and lion manes#

hair serves to insulate, to conceal, to signal, to protect, and to sense the immediate surroundings. Insulation serves to conserve heat, but can protect against excessive heat eg camel

Tenrec

•Tenrec ecaudatus(tailless tenrec)

•The common tenrec occurs on Madagascar and on the Comoro Islands, between Madagascar and Africa.

• Pelage is not dense and is a combination of hairs and blunt spines.

Spiny Anteaters

Echidnas, genus Tachyglossus, subclass Holotheria.

monotreme found only in Australia

and New Guinea. lays a single egg that is

kept in her pouch for seven to ten days until spines begin to harden

• Pelage a mixture of spines and quills

Hair on Humans Filamentous growth from the skin Mainly in mammals; genus definition Function head: protective,

ornamentaleyelashes: protect eyes from dusteyebrows: shield eyesaxillae; wicking of sweat

scalp palmsaxillae solespubes penischest labiabeard fingers

mucus membranes Naked ape

terminal hair

bareeverywhere else covered in vellus hair

Naked Ape

Great apes have sparse and bare areas but none extensiveWhy is man different????1). Adaptation; cool forest to hot savana bipedal

locomotion upright stancebut other cursorial apes, eg gorilla, chimpanzee, no lossape pelage shields from UV, wind, radiant heat

2). Eco-parasites; fitness cost high cohabitation, communal living but other gregarious apes, eg chimpanzee, no loss

3). Aquatic ape; 5-7 e6 yr BC, Danakil region Ethiopiaextended period wading lifestyle

hair loss and subcut. fat more efficient theory not account for eccrine gland, density same as gorilla an chimp but developed for sweat production

Neoteny

paedomorphism slowing of certain aspects of physiological development retention by adults of juvenile physical characteristics dogs share many physical features of immature wolves Louis Bolk 1926: "man is a primate fetus that has become

sexually mature" advocated by; Desmond Morris: The Naked Ape

Stephen Jay Gould: chimp bone brain 4 fold increase in hominid brain size over past 3e6 years loss of body hair a side effect

Types of Hair

Languno: fine hair covers nearly entire embryo

Vellus: poorly pigmented, short, peach fuzz growing most areas

Terminal: fully developed, longer, coarser thicker and darker

Middle ear hair

Although vellus hair continues to develop and accounts for 6% to 25% of scalp hair, it is less noticeable because of its light pigmentation

Depth

vellus follicles situated high in the dermis

large terminal follicles rooted deep in the subcutaneous fat

Dermis

Variable Skin

The density of hair and the numbers of associated eccrine glands varies with different situations in the body

Hair Growth

Hair elongates from the dermal papilla

Length And Growth Rate

Length of hair and growth rate per day vary for each site on the body

hairs on the head 70cm / 0.35mm Eyebrows 3cm / 0.15mm beards and whiskers 28cm / 0.4mm armpit hairs 8cm / 0.3mm pubic hairs 10cm / 0.2mm

Normal Hair Growth

Cyclical pattern

Anagen = growth phase2.5 – 3

yearsCatgen = shortTelogen = resting 100

days

asynchronous

anagen1000 days

catgen

Telogen100 days

Growth Cycle

• 100 to 150,000 follicles on the scalp

• ~95% of them are in an active growth phase called Anagen

• ~5% completed their growth phase

• Telogen hairs typically remain in the scalp for about three months before they are shed.• shampooing, combing or brushing typically releases hair at a rate of about 50 to 80 per day.

Functions of Human Hair

head hair for insulation and protection; trauma UV

eyelashes blink to prevent entry into eye eyebrows, like awnings, protect the eyes from

sunlight and sweat that might be hazardous body hair for insulation; goose bumps

traps air residual?

axilla; wicking of sweat long hair; marker of health?

secondary selection

Inner Ear Hair

Hairs in the ampullae of the semi-circular canals are responsible for balance

Otoliths, crystals of calcium carbonate, floating in gelatinous medium of the saccule brush against the stereocilia of the inner ear. This movement generates stereotypic awareness

Hair Colour

Two types of melanin account for all possible hair colors:Eumelanin: colors hair brown to black Pheomelanin: an iron-rich pigment

colours hair yellow-blonde to red

Both made from amino acid tyrosine, by tyrosinase. Increased tyrosinase activity results in darker hair color

Melanocytes in the hair bulb contain subcellular organelles melanosomes; synthesize and store melanin.

Melanocytes deliver the melanosomes to keratinocytes, where they are incorporated into the growing hair shaft

Long Hair

anthropologists speculate functional significance of long head hair may be adornment

byproduct of secondary natural selection once other somatic hair had been lost

or Fisherian runaway sexual selection;lustrous hair is a visible marker for a health waist length hair = ~1 m or 39 inches long

~80 months, 7 years, to grow long period of nutrition stability hygiene

explain why long hair attractive both sexes

straight hair is round

Shape Affects Curls

curly hair is flattened

Hair Structure

medulla = central core of cuboidal cells

cortex = highly packed cells

cuticular scale = outer layer

Follicle The hair follicle consists of two coats—an outer or dermic,

and an inner or epidermic. The outer or dermic coat is formed mainly of fibrous tissue;

it is continuous with the dermis, is highly vascular, and supplied by numerous minute nervous filaments.

Dermal coat consists of three layers The most internal is a hyaline basement membrane, well-marked only in the larger hair follicles, it is limited to the deeper part of the follicle

Outside this is a compact layer of fibers and spindle-shaped cells arranged circularly around the follicle; this layer extends from the bottom of the follicle as high as the entrance of the ducts of the sebaceous glands.

Externally is a thick layer of connective tissue, arranged in longitudinal bundles, forming a more open texture and corresponding to the reticular part of the dermis; in this are contained the blood vessels and nerves.

Keratins

A long-chain protein of >300 residues contain a high proportion glycine H

smallest amino acids alanine methyl sterically-unhindered hydrogen bonding between the amino and carboxyl groups peptide bonds on adjacent protein chains closely aligned and tightly bound fibres tertiary structure: fibres twisted in helical filaments second in stength to chitin in organic molecules

side chains

tight-helices

Keratin Secondary Structure

keratin molecules > 300 residues high proportion of smallest of

amino acids; glycine H side group alanine, methyl side group.

sterically-unhindered hydrogen bonding between the amino and carboxyl groups of peptide bonds on adjacent protein chains

close alignment and strong binding between chains

keratin molecules twist around each other to form helical intermediate filaments.

Keratin Tertiary Structure

keratin molecules twine around each other in a left-hand helix coil structure

two helices in turn form another left rotating helical fibre, called a protofibril

eight protofibrils form a circular or square structure, called a microfibril, that is the basis of the structure of hair.

This structure is stretchy and flexible and can be compared to a rope containing various threads that are twined together.

The Arrangement of Fibres

• The a-helix coiled keratin molecules are wound together in protofibrils.• protofibrils are bound

together into microfibrils

• Bundles of microfibrils are stitched together to make macrofibrils

• Each hair is wrapped in a cuticle made up of protein scales and contains macrofibrils embedded in matrix proteins

Interchain Bonding

In addition to intra- and intermolecular hydrogen bonds, keratins have large amounts of the sulfur-containing amino acid cysteine ~14%

disulfide bridges confer additional strength rigid, permanent, thermally-stable crosslinking

similar to sulfur bridges in vulcanized rubber

disulfide bonding contributes to insolubility of keratins

pungent smells of burning hair and rubber due to the sulfur compounds formed

Strength

Intra- and intermolecular hydrogen bonds disulfide bridges that confer additional strength and

rigidity by permanent, thermally-stable crosslinking It can be made to curl ’permanently’ or set

temporarily. The breakage and reseting of the interchain bonds allow hair to regain its shape. Hair can stretched about 70%.

Cross-linking creates strength. Hair is equivalent in strenght to iron wire. A wound strand of 5 mm can withstand a weight of 60kg

Static

The close connections of chains is associated with the hair's ability to become charged with static electricity.

keratin is a good insulator of heat and electricity

The capacity to hold an electric charge is refered to as triboelectric

Styling

hair heated with steam and pulled breaks the relatively weak hydrogen bonds the a-helices

The a-helices can elongate without breaking the molecules

• matrix proteins form a tangled supporting mechwork linked by many disulphide bridges. These bridges are also disrupted with moist heat• new interchain hydrogen bonds and disulphide bridges are formed after styling to keep the hair in its new style

Nails Growth

Nail

Growth occurs from a nail bed over a keratin matrix layer

Nail Keratin

Nailbed The nailbed is an essentially parallel epidermal structure located directly beneath the fingernail formed with parallel lines spaced at intervals. During normal growth, the fingernail travels over the nailbed.

The nail is also composed of keratin microfibrils but the molecules are arranged in flat B-pleated sheets

Nails Arranged in Stacks

The molecules of b-keratin in finger and toe nails are organised in sheets stacked in layers. The proteins still fall into two groups; the helical and matrix, but in nail there is less sulphur in the matrix than in the hair matrix.

Hair Length

Sexual selection; visible marker of health

1.25 cm / 0.5 inch per month: good hygiene39 cm = 7 years nutrition

healthstabilty

Dimorphism

• male androgens at puberty

• testosterone

• vellus - terminal hair

• affects growth rate

weightlength

androgen sensitivity

Hair and Culture

Much variation in style and length in different times and places

Egypt head hair shaved, especially children long single lock of hair growing

Middle ages: shaved head + wig 17 to 18th C: long hair

eg Cromwell Napoleon

Washington

WWI: lice and fleas brought typhus, short hair adopted

Maasai warrior

Body Hair

attitudes towards hair on the human body also vary between different cultures and times

some cultures excessive chest hair on men is a symbol of virility and masculinity, other societies display a hairless body as a sign of youthfulness

ancient Egypt, people regarded a completely smooth, hairless body as the standard of beauty

adopted Greeks; hairless body = youth and beauty (strigyl)

Islam; many hair tenets, five traits of fitrah Western societies; removal, bikini fashion,

‘manscaping’

Hirsutism

Hormonal changes alter hair presence and thickness

Vellus hairs on face of women,

invisible/inconspicuous

Oestrogen, antagonist of DTH

Menopause; thicker and darker

Diseases;

Polycystic ovary syndrome

Cushing's disease

ovarian or adrenal gland tumors

Hair Loss

 Whales & porpoises, and walrus use blubber for insulation.

 Elephants, rhinos, hippos - warm climate, favorable mass/surface ratio -> retention of heat no problem.

molt = continuous or seasonal (1 or 2x /year) hair replacement

seasonal fur color change: arctic fox, hares, some weasels

Hair Loss

caused by range of factors; genetic agingskin conditionsdiseases medications, eg anti-cancer drugs.mechanical damageskin infections.

The followings are the most common Alopecia areata Telogen effluvium Alopecia androgenica = Male Pattern Hair Loss

Alopecia androgenica

characterized by "receding hairline" from lateral sides of the forehead

follicular miniaturization, shaft width decreases becoming fragile

30% males by 50 yrs 50% by 65 years66% of adult males

largely genetically determined caused by male hormones or

androgens esp DHT

Male Pattern Baldness

occur in varying forms in about 66% of adult males at some point

characteristic (i) receding hair from lateral forehead stages; (ii) bald patch develops on vertex (iii) coalescence of patches

pattern baldness is classified on the Hamilton-Norwood scale I-VIII

Process of Balding

In presence of DTH in genetically prone men, hair undergoes progressive thining;

- the anagen growth phase is shortened so the hair is shorter when it stops growing- overseveral life cycles progressive follicular miniaturization decreases shaft width and hair becomes thinner and shorter

Treatments

Finasteride (marketed in the U.S. as Propecia) Minoxidil (marketed in the U.S. as Rogaine) Saw Palmetto (Serenoa repens) is an herbal DHT

inhibitor

easier to prevent the aging and falling out of healthy hairs than to regrow hair

Alopecia Areata

characterized by patchy scalp hair loss

many as 1 in 1,000 people some time

most common causes are medications, pregnancy, birth control pills, thyroid malfunctions, anemia, syphilis, and arthritis

autoimmune response, immunological rejection, anti-follicular

Often resolves spontaneously 50% of people will have recurrence

Cyclosporins may have dramatic effects but are usually temporary

careful review of your medical history

Alopecia Universalis

• complete loss of hair from all site of body

• some are born with some hair but begin losing it quickly

• can be inherited as an autosomal recessive trait. • traced to mutation in a gene dubbed HR in chromosome band 8p21.2. human homologue of mouse "hairless" gene

• Several families known where hairlessness passed through 3 generations

Telogen Effluvium

characterized by sudden diffuse hair loss

general thinning of the hair over a period of months

most commonly experienced by those who have just given birth, or are undergoing chemotherapy

Also caused infection, severe chronic illness, severe psychological stress, majorsurgery, hyperthyroidism, Crash Diets resulting in poor health or inadequate protein, and medications

Trichotillomania characterized by incessant

pulling or plucking of one's own hair

tillein Greek for "to pluck, pull out children, males most commonly

in adulthood and adolescence, most patients are females

hair manipulations usually occur sedentary activities, reading, writing, or watching television

impulse control disorder mental state characterized by

tension with gratification or relief from the hair pulling

once the behavior is established, it becomes habitual, regardless of the initial causative emotional problem

Resolution requires psychological intervention

Tinea Capitis

infection characterized by bare patches of skin on the scalp

fungal infection of the skin of the scalp, eyebrows and eyelashes

most commonly found in children ages 10 and under,

scaly non-inflamed area of skin seborrheic dermatitis

person-to-person transmission. The organism remains viable on combs, brushes, couches, and sheets

Since effective treatment of Tinea Capitis by griseofulvin in the 1950s incidence dropped from 14% to 1.2%

Aging

pigment in the hair is lost, hair becomes colourless time varies from person to person men tend to become grey at younger ages than

women pale blond hair becomes white instead of grey

red hair becomes a sandy color and later white gray or white appearance due to air bubbles in

medula scattering light scalp hair loss or thinning with aging in both sexes half of all men are affected by male pattern

baldness by the time they are 50

Death

It is commonly claimed that hair and nails will continue growing for several days after death.

This is a myth; the appearance of growth is actually caused by the retraction of skin

as the surrounding tissue dehydrates, nails and hair become more prominent

Histological Prep

Crossectional View

medullacortex

cuticle

dermal sheath

epidermal sheath